The regulation of cells and tissues is controlled by autocrine and paracrine factors, such as systemic hormones and factors that modulate or mediate the action of hormones.
Many peptides, expressed locally, can influence certain biological activity in the mammalian system and are very important in the regulation of cells of the epithelium. These factors largely have not been identified or characterized, particularly not in humans.
A few factors that play a role in the regulation of functions of the lung and uterus, both adult and fetal, have been identified in non-human organisms. One such factor is mammalian CC10, i.e., human, rat and rabbit CC10. (Wolf, M. et al., Human Molecular Genetics, 1(6):371–378 (1992)). Clara Cell 10 kDa secretory protein (CC10) which is also called Clara Cell 17 kDa protein, is a homodimer consisting of 8.5 kDa monomers that are joined by two disulfide bonds (Umland, T. C. et al., J. Mol. Biol., 224:441–448 (1992)). It is the predominant secreted protein of lung Clara cells which are the lining of the bronchiolar epithelium (Singh, G. and Katyal, S. L., J. Histochem. Cytochem., 32:49–54 (1984)). The physiological role of the protein is not yet completely understood. It has been reported that CC10 specifically binds methylsulfonyl-polychlorated biphenyls (PCBs) (Nordlund, Moler, L. et al., J. Biol. Chem., 265:12690–12693 (1990)) and inhibits phospholipase A2 (Singh, G. et al., Biochem. Biophys. Acta, 1039:348–355 (1990)). In the last few years the sequences of rat (Katyal, S. L. et al., Prog. Respir. Res., 25:29–35 (1990); and Hagen, G. et al., Nucleic Acids Res., 18:2939–2946 (1990)), and human (Singh, G. et al., Biochem. Biophys. Acta, 950:329–337 (1988) CC10 cDNAs have been reported. cDNAs, and the derived amino acid sequences, show striking homologies to rat uteroglobin (Singh, G. et al., Biochem. Biophys. Acta, 1039:348–355 (1990); and Hagen, G. et al., Nucleic Acids Res., 18:2939–2946 (1990)).
Like CC10, rat uteroglobin is a covalently bound homodimer whose three dimensional structure is well known (Morize, I. et al., J. Mol. Biol., 194:725–739 (1987). Uteroglobin expression in rabbits has been originally reported in the uterus during the preimplantation phase (Beier, H. M., Biochem. Biophys. Acta, 160:289–290 (1968)). More recently, the protein was also detected in oviduct (Kirchner, C., Cell Tissue Res., 170:490–492 (1976)), male genital organs (Beier, H. M. et al., Cell Tissue Res., 165:1–11 (1975)), esophagus (Noske, I. G. and Feigelson, M., Biol. Reprod., 15:704–713 (1976)) and lung (Noske, supra; and Torkkeli, T. et al., Biochem. Biophys. Acta, 544:578–592 (1978)).
In vitro, several distinct properties of uteroglobin have been described. Soon after its discovery it could be shown that the steroid hormone progesterone is specifically bound by the protein (Beato, M. and Baier, R., Biochem. Biophys. Acta, 392:346–356 (1975); and Beato, M. et al., J. Steriod Biochem., 8:725–730 (1977)). Therefore, rabbit uteroglobin was believed to be a potential carrier or scavenger of progesterone that regulates the progesterone concentration in the endometrium (Atger, M. et al., J. Steroid Biochem., 13:1157–1162 (1980)). It has also been shown to specifically bind certain methylsulfonyl metabolites of polychlorinated biphenyls with even higher affinity than progesterone (Gillner, M. et al., J. Steroid Biochem., 31:27–33 (1988)). Furthermore, uteroglobin has been found to inhibit phospholipase A2. The relationships of all these properties and their physiological significance is still not understood and remains largely a matter of speculation.
The rat CC10 mRNA is expressed like rat uteroglobin not only in lung but also in the esophagus as well in uteri of estrogen and progesterone treated female rats (Hagen, G. 1990 supra) suggesting that rat CC10 is the rat counterpart of rat uteroglobin (see in general Wolf, M. et al., Human Molecular Genetics, 1(6):371–378 (1992)).
Human CC10 expression is abundant in non-neoplastic human lung, and it is detectable in tumors in corresponding cell lines at markedly lower levels (Broers, J. L. V. et al., Lab. Invest., 66:337–346 (1992); Linnoila, R. I. et al., Amer. J. Clin. Pathol., 90:1–12 (1988)). CC10 levels were also significantly lower in 6 serum and bronchoalveolar lavage specimens obtained from smokers and lung cancer patients compared with specimens from healthy non-smokers (Bernard, A. et al., Europ. Resp. J., 5:1231–1238 (1992)). These findings suggest the expression of CC10 mRNA becomes altered in distinct lung compartments and may implicate a role for CC10 in the development of pulmonary carcinomas (Jensen, S. M. et al., Int. J. Cancer, 58:629–637 (1994).
Some of the biological properties of UG, such as masking the antigenicity of blastomers (Mukheijee, A. B., et al., Med. Hypotheses, 6:1043–1055 (1980)) and epididymal spermatozoa (Mukherjee, D. C., et al., Science (Wash. D.C.), 219:989–991 (1983)), inhibition of monocyte and neutrophil chemotaxis and phagocytosis in vitro (Schiffman, E. V., et al., Agents Actions Suppl., 12:106–120 (1983)), and inhibition of ADP- and thrombin-induced (but not of arachidonic acid-induced) platelet aggregation (Manjunath, R., et al., Biochem. Pharmacol., 36:741–746 (1987)), may be due, at least in part, to the potent inhibitory effect of this protein on PLA2 activity (Levin, S. W., et al., Life Sci., 38:1813–1819 (1986)). A nonapeptide derived from the amino acid sequence of .alpha.-helix-3 of UG monomer (residues 39–47) possesses all the biological properties of the intact protein and has been identified as an active site of UG responsible for its PLA2-inhibitory and antiinflammatory activities (Miele, L., et al., Nature (Lond.), 335:726–730 (1988)).
It has been indicated that cclOkD-specific transcripts are present in several nonrespiratory human organs and tissues. By using an antibody to rabbit UG, a UG-like immunoreactivity in human endometrium (Kikukawa, T., et al., J. Clin. Endocrinol. Metab., 67:315–321 (1988)), prostate (Manyak, M. J., et al., J. Urol., 140:176–182 (1988)), and respiratory tract (Dhanireddy, R., et al., Biochem. Biophys. Res. Commun., 152:1447–1454 (1988)), has been described.
Recently, the cDNA (Singh, G., et al., Biochem. Biophys. Acta, 950:329–337 (1988)) and the 5′ regions (Wolf, M., et al., Human Mol. Genet., 1:371–378 (1992)) of the gene encoding human uteroglobin (hUG), a counterpart of rabbit UG (rUG), has been characterized. Human UG or Clara cell 10-kD protein has 61.5% amino acid sequence identity with rUG (Singh, G.,.et al., Biochem. Biophys. Acta, 950:329–337 (1988)), 54.2% similarity with rat UG (Singh, G., et al., Biochem. Biophys. Acta, 1039:348–355 (1990)), and 52.8% with mouse UG (Singh, G., et al., Exp. Lung Res., 19:67–75 (1993)). Although this protein was originally discovered in the alveolar Clara cells (Singh, G., et al., J. Histochem., 36:73–80 (1988)) it is detectable in many extrapulmonary tissues similar to the ones in which rUG is expressed (Peri, A., et al., DNA Cell Biol., 5:495–503 (1994)) and this expression is induced by progesterone. It appear that some of the biological properties of hUG are virtually identical to rUG (Mantile, G., et al., J. Biol. Chem., 27:20343–20351 (1993)).
It has been reported that UG in the rabbit uterine fluid is first detectable on day 3 of pregnancy, and peak level is reached on day 5 (for a review see Miele, L., et al., Endocr. Rev., 8:474–490 (1987)). UG, by inhibiting PLA2 activity, may down-regulate the production of proinflammatory lipid mediators, which promote contraction and motility of the uterine smooth muscle. Therefore, it is suggested that UG facilitates the maintenance of myometrial quiescence during gestation.
There is a clear need in the art to further isolate and characterize proteins which are homologues of mammalian Clara cell 10 kDa secretory protein and rat prostatic steroid-binding protein. The genes and gene products of the present invention display homology to the rat prostatic steroid-binding protein and Clara cell 10 kDa secretory protein.